Year by year, improvements have been sought after in a semiconductor integrated circuit with respect of high-speed performance, power saving and high integration. Thus, in recent years, it has come to be demanded that wiring resistance is reduced by employing a copper wiring, and as well the dielectric constant of an insulator (insulator film) interposed between wiring lines is reduced (reduction in Low-k value), thereby reducing parasitic capacitance between the wiring lines. The insulator is formed as a thin film on a surface of a semiconductor substrate. There has been proposed a thin-film inspection apparatus in which a thin film formed on a crystalline substrate such as a semiconductor element is irradiated with X-rays, and inspection is carried out by receiving the resultant small-angle reflection beam (e.g., refer to Japanese Unexamined Patent Publication JP-A 60-88341 (1985)). In the publication it is disclosed that the reason why the small-angle reflection beam is used is that since a small-angle beam is allowed to travel a relatively long distance even if the film is made thin, information can be acquired from within the thin film with sufficient sensitivity.
In an attempt to attain a Low-k characteristic, at first, development was carried out to produce a substance, as a material used as an insulator, that exhibits a low dielectric constant on its own. After that, in order to achieve further reduction in dielectric constant, the following technique is being ready for commercial use: forming minute and uniform pores in an insulator to make the insulator a porous body, so that the effective dielectric constant of the insulator itself may be reduced.
However, such a porous body may exhibit pore-size distribution variation. In particular, due to the presence of an extraordinary large pore (killer pore), mechanical properties may be vulnerable, with the result that the porous body is no longer able to withstand a process step subsequent to the formation of the insulator film, or that a metal material of a metal film, which is formed in a subsequent process, finds its way into the killer pore so as to cause damage to the electrical characteristics. Furthermore, the pore size distribution varies with the conditions set for the formation of the insulator film, such as a temperature condition. Therefore, in terms of applying the low dialectic constant porous body to a semiconductor integrated circuit, it is a significant challenge to measure and confirm whether the pore size distribution of the formed insulator film is kept at a predetermined level or not.
As techniques for measuring the pore size distribution (size probability distribution), there have been used a small-angle X-ray scattering method, a small-angle neutron scattering method, etc. For exercising control on integrated-circuit production process, increasing attention has been paid to the small-angle X-ray scattering method that allows easy measurement in semiconductor production facilities. There have been known some techniques for performing pore size distribution measurement based on the small-angle X-ray scattering method without using synchrotron radiation (e.g., refer to “Denshi Zairyo (Electronic Materials)”, pp. 56-60, issued in May 2001 by Kogyo Chosakai Publishing Co., Ltd). What described in “Electronic Materials”, pp. 56-60, issued in May 2001 by Kogyo Chosakai Publishing Co., Ltd is a reflective small-angle X-ray scattering measurement method based on an offset scanning technique.
In order to achieve the small-angle X-ray scattering measurement with high accuracy, it is important to keep the wavelength of a to-be-irradiated X-rays and the direction aligned. A spectroscope is used to monochromatize and converge X-rays. It has been known as a method for forming a spectroscope to deposit multi-layer films in which the surface interval is so controlled as to satisfy Bragg's rule (e.g., refer to Japanese Unexamined Patent Publication JP-A 8-220027 (1996))). Moreover, there has been proposed a technique to realize high-precision in an X-ray optical apparatus by adopting a multi-layer mirror having an ellipsoidal reflection surface as a spectroscope (e.g., refer to Japanese Unexamined Patent Publication JP-A 2001-356197).
FIG. 32 is a schematic view showing an X-ray scattering angle involved in the offset scanning technique. According to the offset scanning technique, X-rays R enter the surface of a specimen 31 at an incident angle of θi, and the resultant reflection light (scattered light) exiting therefrom at a detection angle of θe is detected. With the detection angle θe maintained larger by a predetermined offset angle 2θo than the incident angle θi, the incident angle θi and the detection angle θe are continuously varied. Note that the scattering angle 2θd is given by: 2θd=θi+θe.
FIG. 33 is a constitution diagram schematically showing the structure of a measurement apparatus designed for use with the reflective small-angle X-ray scattering measurement method based on the offset scanning technique. In a spectroscope 33 are selectively spectralized certain components of X-rays R emitted from a linear focus X-ray tube 32 having desired wavelengths. As the spectroscope 33, a crystalline spectroscope or a multi-layer film spectroscope is employed. In the spectroscope, the X-rays are reflected intensely only in a case where the incident angle and the exiting angle with respect to the crystalline surface are equal to each other and also GLAG law is satisfied. The spectroscope 33 is so determined that a spectral component traveling toward the specimen 31, i.e. a measurement target object, enters the specimen 31 through a solar slit 34. Of the X-rays R, only the specific direction component is allowed to pass through the solar slit 34.
The X-rays reflected from the specimen 31 enter an X-ray detector 37 through a solar slit 35 and a light-receiving slit 36. Of the X-rays, only the specific direction component is allowed to pass through the solar slit 35. The light-receiving slit 36 is arranged for the purpose of allowing only the X-rays having a specific exit angle to enter the X-ray detector 37.
In the measurement apparatus shown in FIG. 33, the incident angle θi of the X-rays R is changed by varying the angle of a non-illustrated table on which the specimen 31 is emplaced. Moreover, the detection angle θe is changed by varying the angle of the light-receiving surface of the X-ray detector 37.